Transcription of repeat DNA in vitro by RNA polymerase III in cytosol extracts is inhibited when the extract is of the same species as the DNA

Cytosol extracts containing RNA Polymerase III were obtained from cultured human (HeLa) and bovine (MDBK) cells. Human extract efficiently transcribed genomic bovine DNA and cloned bovine alu-type repeat DNA while genomic human DNA and cloned human alu repeat DNA were inefficient templates. Conversely, genomic bovine DNA and cloned bovine alu-type repeat DNA were less effective templates for bovine extract than were genomic human DNA and alu repeat DNA. These results suggest that species specific factor(s) present in mammalian cells are responsible for the observed in vivo inhibition of transcription of most alu-type repeat DNA.